180
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Fieldbus Communication
ETHERNET
WAGO-I/O-SYSTEM
750
BACnet/IP Controller
Attention
Never set all bits to equal 0 or 1 in one byte (byte = 0 or 255). These are re-
served for special functions and may not be allocated. Therefore, the address
10.0.10.10 may not be used due to the 0 in the second byte.
If a network is to be directly connected to the Internet, only registered, inter-
nationally unique IP addresses allocated by a central registration service may
be used. These are available from Inter
NIC
(International Network Informa-
tion Center).
Attention
Direct connection to the Internet should only be performed by an authorized
network administrator and is therefore not described in this manual.
Subnets
To allow routing within large networks a convention was introduced in the
specification
RFC 950
. Part of the Internet address, the subscriber ID is di-
vided up again into a subnetwork number and the station number of the node.
With the aid of the network number it is possible to branch into internal sub-
networks within the partial network, but the entire network is physically con-
nected together. The size and position of the subnetwork ID are not defined;
however, the size is dependent upon the number of subnets to be addressed
and the number of subscribers per subnet.
1
8
16
24
32
1 0
Net-ID
Subnet-ID
Host-ID
Fig. 4-10: Class B address with Field for Subnet ID
Subnet mask
A subnet mask was introduced to encode the subnets in the Internet. This in-
volves a bit mask, which is used to mask out or select specific bits of the IP
address. The mask defines the subscriber ID bits used for subnet coding,
which denote the ID of the subscriber. The entire IP address range theoreti-
cally lies between 0.0.0.0 and 255.255.255.255. Each 0 and 255 from the IP
address range are reserved for the subnet mask.
